This invention relates to elongate, closed-shell air depolarized electrochemical cells. This invention is related specifically to metal-air air depolarized electrochemical cells illustrated herein as elongate cylindrical cells, and is described herein in relation to cells having the size generally known as xe2x80x9cAA.xe2x80x9d
The advantages of air depolarized cells have been known as far back as the 19th century. Generally, an air depolarized cell draws oxygen from air of the ambient environment, for use as the cathode active material. Because the cathode active material need not be carried in the cell, the space in the cell that would have otherwise been required for carrying cathode active material can, in general, be utilized for containing anode active material.
Accordingly, the amount of anode active material which can be contained in an air depolarized cell is generally significantly greater than the amount of anode active material which can be contained in a 2-electrode cell of the same overall size. By xe2x80x9c2-electrodexe2x80x9d cell, we mean an electrochemical cell wherein the entire charge of both anode active material and cathode active material are contained inside the cell structure when the cell is received by the consumer.
Generally, for a given cell size, and similar mass, an air depolarized cell can provide a significantly greater number of watt-hours of electromotive force than can a similarly sized, and similar mass, 2-electrode cell using the same, or a similar, material as the anode electroactive material.
Several attempts have been made to develop and market commercial applications of metal-air cells. However, until about the 1970""s, such cells were prone to leakage, and other types of failure.
In the 1970""s, metal-air button cells were successfully introduced for use in hearing aids, as replacement for 2-electrode cells. The cells so introduced were generally reliable, and the incidence of leakage had generally been controlled sufficient to make such cells commercially acceptable.
By the mid 1980""s, zinc-air cells became the standard for hearing aid use. Since that time, significant effort has been made toward improving metal-air hearing aid cells. Such effort has been directed toward a number of issues common to all manufacturers of such cells. For example, efforts have been directed toward increasing electrochemical capacity of the cell, toward consistency of performance from cell to cell, toward control of electrolyte leakage, toward providing higher voltages desired for newer hearing aid technology, toward higher limiting current, and toward controlling movement of moisture into and out of the cell, and the like.
While metal-air button cells have found wide-spread use in hearing appliances, air depolarized cells have not had wide-spread commercial application for any other end uses, or in other than small button cell sizes.
The air depolarized button cells readily available as items of commerce are generally limited to sizes of no more than 0.6 cm3 overall volume. In view of the superior ratio of xe2x80x9cwatt-hour capacity/massxe2x80x9d of air depolarized cells, it would be desirable to provide air depolarized electrochemical cells for other applications. It would especially be desirable to provide air depolarized electrochemical cells which are relatively much larger than button cells. For example, it would be desirable to provide such cells in xe2x80x9cAAxe2x80x9d size.
It is an object of the invention to provide an air depolarized cell which is relatively larger than a hearing aid button cell and which has a greater overall discharge cycle capacity than a similarly-sized alkaline manganese dioxide cell.
It is another object to provide an air depolarized cell which is relatively larger than a hearing aid button cell, which has an overall discharge capacity at least as great as a similarly-sized alkaline manganese dioxide cell, and wherein the energy/mass ratio of such cell is significantly greater than the energy/mass ratio of a similarly-sized alkaline manganese dioxide cell.
The invention contemplates an air depolarized electrochemical cell, having an outer surface, the cell comprising an anode; a cathode, including an air cathode assembly defining at least a portion of the outer surface of the cell; and a separator between the anode and the cathode.
In some embodiments, the cell further comprises a bottom member defining a bottom of the cell, and a top member defining a top of the cell, the air cathode assembly extending between the bottom member and the top member, and defining a portion of the outer surface of the cell between the bottom member and the top member.
In some embodiments, the cell further comprises an anode cavity defined inwardly of the separator and upwardly of the bottom member, and a mass of electroactive anode material in the anode cavity.
Preferred embodiments include an elongate anode current collector extending into the mass of electroactive anode material, and in electrical contact with the mass of electroactive anode material.
In some embodiments, the top member comprises a top contour washer having inner and outer downwardly depending legs receiving an upper edge portion of the cathode assembly in a slot therebetween, and an insulating grommet in the slot, electrically insulating the cathode assembly from the top contour washer.
In some embodiments, the top member comprises a top contour washer having inner and outer downwardly depending legs receiving an upper edge portion of the cathode assembly in a slot therebetween, and a seal grommet in the slot, the combination of the top contour washer and the seal grommet providing a seal impeding leakage of electrolyte around the upper edge portion of the cathode assembly and thence out of the cell.
A second expression of the invention is embodied in an air depolarized electrochemical cell, comprising an anode; a cathode, including an air cathode assembly, the air cathode assembly comprising an air diffusion member, at least a portion of the air diffusion member being openly exposed to the ambient environment; and a separator between the anode and the cathode.